Help with this flash please

I've got a Vivitar 3700 Auto Thyristor but I don't really know how to use it. It'll be used on my eos 1-n as I've done in the past with decent results as a bounced flash. I intend to use it this time in a hospital room as a bounced flash and tmy-2 rated @400. I'd like to shoot at f2 around 1/90 or 1/125. Like I said, I've gotten decent results using this combo at a couple weddings but I don't remember how I had it set up. I may add a small white card to the flash for an eye light as well.
What should I set the buttons to on the flash?
Should I go with shutter speed priority on the camera?


vinny

I assume you're looking to use the "auto" function within the flash. If so:

Set the ISO as desired on both the top and bottom scales of the flash.
Determine distance
Set the f-stop on your lens to match one of the 3 auto settings (red, blue, orange), making sure that setting includes the distance of your subject
Set the sliding switch on the bottom to match the auto setting you used to determine f-stop

So, for example, with a flash to subject distance of 20 feet:
Note that 20 feet falls within the red and blue settings, but outside the orange setting
Choose an f-stop of 5.6 or 11 (note that this is with an iso of 800)
If you choose f/11, set the sliding switch on the bottom to red
If you chose f/5.6, set the sliding switch on the bottom to blue

Another way to look at it is that with iso 800, an f-stop of 11, you will have adequate flash lighting up to 30 ft. With ISO 400, probably f/5.6. If you want a wider aperture, choose the red setting and the appropriate f-stop. You will then effectively use the flash at some % of it's full power.

But keep in mind that this is a very crude average value. So easily fooled by very light or very dark walls behind the subject. Also, keep in mind that distance is the distance light travels, so basically double the distance if bouncing.

If this isn't what you meant, and I've typed all this for nothing, just humor me.

Your shutter speed on the camera will be determined by the camera's limitation for flash synch - someone more familiar with the eos 1-n will likely know what the maximum speed is. I know that with my Olympus OM bodies, I cannot use anything shorter than 1/60.

Otherwise, it is as mgb74 suggests.

If there is a test flash button (possibly the LED beside the lightning bolt) you can point the flash at your subject and press that and if there is enough light for the auto flash function to be satisfied, the green LED at the bottom will light and/or flash. As mgb74 indicates, this can give you a false positive if the background and surroundings are much lighter than average.

Hope this helps.

Matt

P.S. I've just checked the info on wikipedia for your camera, and it indicates a maximum x-synch speed of 1/250

Well, I know the walls will be off white or grayish, the ceilings about 9 feet and my subject distance no more than 8 feet. I'd like to use the flash for fill, not to overpower the existing lighting in the room. Should the camera be in manual mode or shutter priority? If show can I still shoot @ 1/90?
What about the flash compensation on the camera? In the past I've always set it to -1. By the looks of it @ 400asa I can't set the flash to lets say 15ft and still shoot @f2.
What about adding neutral density gel (I have everything from 1/2 stop to 3 stops) to the flash and calculating that in?
What's manual mode on the flash do to the output?

Manual will give you full output of the flash when it fires. Usually slower recycle time too.
Do you intend to bounce from the ceiling or from a card? If you use the ceiling, your distance becomes greater. IE flash to ceiling and then ceiling to subject. If from a card it's pretty much ignored.

Ceiling bounce.
anybody else?

Please?

mgb74, Matt and John said it all.
What else is there?

Set both the flash's ISO scales.

Select an aperture according to the three auto settings available, based on the estimated distance (via ceiling).

Select the flash's auto mode accordingly.

Set that same aperture on your lens.

Set a shutterspeed that allows flash synch (with the camera in manual mode).
If the ambient light is too strong for that aperture and the fastest shutterspeed that allows flash synch, go to a smaller aperture + auto mode. But that may mean your flash won't reach anymore - if so, nothing you can do about it, except not bounce, or dim the ambient light so you do not need to change aperture.


And when shooting the first shot, keep an eye on the lighton the back of the flash: if it blinks, you're ok. Else, either select a larger aperture and the auto mode belonging to it, or don't bounce.